How to Install Exchange Server Updates on DAG Members

Applies to: Exchange Server SE / 2019 / 2016 / 2013 / 2010

Exchange Server updates on a Database Availability Group (DAG) should be installed one member at a time. The main goal is to move active databases away from the server, prevent them from activating back during maintenance, install the update, and then return the server to production.

The original version of this article was written for Exchange 2010 SP1 and used the term Update Rollup. Current Exchange Server servicing uses Cumulative Updates (CU), Security Updates (SU), and when required Hotfix Updates (HU). The DAG maintenance principle is still the same.

In This Article

• 1. Before You Start
• 2. Put the DAG Member in Maintenance Mode
• 3. Install the Exchange Update
• 4. Return the Server to Production
• 5. Update the Remaining DAG Members
• 6. Validate After the Update
• 7. Key Takeaways

1. Before You Start

Before patching a DAG member, confirm that the DAG is healthy and that the remaining members can host the active databases while one server is offline.

• Run the Exchange Server Health Checker and review any update or configuration warnings.
• Confirm database copies are healthy and replication is current.
• Check the release notes and prerequisites for the CU, SU, or HU you are installing.
• Reboot the server before the update if required by your maintenance process.
• Make sure you have a current and tested backup of Exchange and Active Directory.

For a CU, Microsoft recommends testing the update before production deployment and running setup from an elevated command prompt. Security Updates should also be installed promptly as they are released.

2. Put the DAG Member in Maintenance Mode

Exchange includes StartDagServerMaintenance.ps1 in the Exchange scripts directory. The script assists with moving active databases away from the selected DAG member, moving critical DAG functions such as the Primary Active Manager (PAM) role, and preventing those functions from moving back while maintenance is in progress.

The scripts are available through the Exchange scripts path represented by $ExScripts. Microsoft documents the ServerName parameter for selecting the DAG member and the WhatIf parameter when you want to review the expected actions first.

Before continuing, confirm that active databases have moved to healthy copies on other DAG members and that the server is no longer serving active mailbox databases.

3. Install the Exchange Update

Install the required Exchange update while the DAG member is in maintenance mode. Exchange services and the Windows Cluster service can be stopped during the installation, which is expected behavior.

For Cumulative Updates, remember that a CU is a full Exchange build. You do not need to install every previous CU first. Security Updates are CU-specific, so after moving to a newer CU, install the latest SU that applies to that CU.

After the update completes, reboot the server even if setup does not explicitly request it.

4. Return the Server to Production

After the server has restarted and Exchange services are healthy, use StopDagServerMaintenance.ps1 to take the DAG member out of maintenance mode and make it available again for database activation and DAG functions.

Do not immediately move databases back just because the server has started. First confirm that Exchange services, DAG membership, database copies, and client connectivity are healthy.

5. Update the Remaining DAG Members

Repeat the same process for each DAG member, one server at a time. Microsoft recommends a rolling update and states that DAG members should run the same Exchange version, including Cumulative and Security Updates. Avoid leaving DAG members on different build levels for an extended period.

After all members have been updated, RedistributeActiveDatabases.ps1 can optionally be used to rebalance active database copies according to activation preference.

6. Validate After the Update

• Confirm all Exchange services that should be running are started.
• Verify DAG membership and database copy health.
• Check that active databases are distributed as expected.
• Review Exchange and Windows event logs for new errors.
• Run the Exchange Server Health Checker again and review any post-update actions.
• Confirm the installed Exchange build matches the intended CU and SU level.

7. Key Takeaways

• Update DAG members one at a time using a rolling maintenance process.
• Put the server into DAG maintenance mode before installing the update.
• Use the Exchange maintenance scripts to move active databases and DAG functions safely.
• Reboot and validate the server before updating the next DAG member.
• Keep all DAG members on the same Exchange CU and SU level.

References

• Microsoft Learn – Manage database availability groups
• Microsoft Learn – Upgrade Exchange to the latest Cumulative Update
• Microsoft Learn – Exchange Server update FAQ